Process of crystallizing dextrose



Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE PROCESS OF CRYSTALLIZING DEXTROSE Application .finie 4, i931, serial No. 146,421

This invention relates to the production of high purity dextrose from starch converted solutions in which the sugar from one crystallizing operation is melted and re-used in another crystallizing operation; the invention being concerned `more particularly with a process in which the converter liquor is given repeated crystallizations and the sugar produced at a later crystallizing stage or stages is used after melting, at an earlier crystallizing stage.

Y The object of the invention is to facilitate the process and improve the purity and crystalline character of the ultimate product by a procedure which reduces to a minimum the quantity of impurities, that is, residual mother liquor, reintroduced into the process through the return and re-use of the melted sugar.

The invention will be described in connection with a two-boiling process in which the second sugar is melted and used for a first sugar crystallization. Obviously the same improvement could be applied to a process involving three or more crystallizations in which the sugar at any late stage of crystallization is re-introduced, in a melted or dissolved state, into the process at an earlier crystallizing stage.

The invention is illustrated in the accompanying iiow sheet which shows the improvement as applied to a two-stage crystallizing process.

Referring to the drawing, A designates the converter in which the starch in suspension in acidulated water is converted to form the usual dextrose solution. The dextrose solution thus made is subjected to a series of treatments, i. e., neutralization, refinement, concentration and cooling, indicated at B before being introduced into the first crystallizer C. The massecuite from crystallizer C is introduced into one or more centrifugal machines, indicated at D, by means of which the major portion of the mother liquor is extracted from the crystals and the residual impurities washed out of the-crystals with fresh water introduced at E; the first greens (the major portion of the mother liquor) passing out of the centrifugal machine into pipe F and the wash water being discharged into pipe G. The washed sugar is the finished product of the process and will have a purity between 99.5% and 100%.

The rst greens are then given certain treatments at H. They may be re-converted and then refined, concentrated and cooled. The reconversion step, however, may be omitted. After these pre-treatments the first greens are introduced into the second crystallizer J and crystallization eiected in the usual manner. The massecuite from the second crystallizer is delivered to the second centrifugals K by means of which the major portion of the mother liquor (hydrol) is extracted, that is, such part of the mother liquor as can be removed conveniently by centrifugal force alone.

'I'he steps as above described are known and the operating data required forpracticing them need not be here given. It has been the practice to melt the second sugar, the sugar from the centrifugals K without giving it the fresh water to which the crystal masses in the first centriiugals D are subjected. The reason for this has been that washing with fresh water involves dissolving a considerable quantity of sugar which, in the case of second sugar. would mean a sugar loss which would be quite considerable because of the relatively low purity of purged but unwashed second sugar, the usual second sugar purities being between 90% and 94%, dry substance basis. If second sugar were washed in the same way that irst sugar is washed, the sugar content of the wash water would have been so high as to entail a serious loss, while the impurity content would have made the wash water practically unusable in the process.

It has been customary, therefore, to run the second sugar, purged but unwashed, to a melter, shown at L on the iiow sheet, where the sugar is melted with Wash water from the first centrifugal D, conducted to the melter through pipe G. The sugar melted at D passes through pipe M back to the process at B where it was mixed with converter liquor from the converter A. however, according to former methods involved returning to the process a considerable quantity of impurities, as has been stated, which either reduced the purity of the ultimate product, the rst sugar, or involved more Washing than would otherwise be necessary. Washing is undesirable, first because of the loss of sugar which it entails, and second, because of erosion which detrimentally ai'fects the brilliancy and luster of the sugar.

According to the present invention, the residual hydrol in Vthe second sugar is displaced at the end of the centrifuging operation by a dextrose syrup consisting principally of dextrose and water, which is introduced into the centrifugal machine after the major portion of the hydrol has been removed, and is forced through the crystal mass by centrifugal action. Preferably this dextrose syrup consists of wash water from the washing of the first sugar which, as shown on the flow sheet, is introduced into the second 5A centrifugal by 'a pipe N shown as a branch of the Wash water pipe G.

The wash liquor used in this connection is a saturated dextrose solution, or approximately so, so that it is not capable of dissolving any considerable amount of the second sugar. Its gravity and viscosity are approximately those of the hydrol in the second sugar. Thus, when introduced into the second centrifugal K, this liquor will displace the .residual hydr l on the faces of the sugar crystals and force the same out oi' the sugar mass into the hydrol outlet O. As a result of the expedient the purity of the second sugar, which is to be melted and returned to the first crystallization, due to the fact that the wash water has a higher purity than the hydrol which it disp/laces, may be increased to 97% or 98% which means the elimination from the system of an appreciable amount of impurities without any substantial loss of sugar substance.

The invention has been described in a preferred embodiment which, however, is to be considered as typical and informative and not limiting the application of the invention to the particular process described. The intention is to cover all equivalents as well as all modifications within the scope of the appended claims.

I claim:

l. Process for the production of crystalline dextrose which comprises: crystallizing a dextrose solution and removing the mother liquor from the crystals; subjecting the mother liquor to a crystallizing operation; centrifuging the massecuite to remove most of its mother liquor; introducing into the centrifugal machine, as a wash liquor for removing residual mother liquor, a substantialiy saturated dextrose solution of higher purity than the residual mother liquor to displace said mother liquor and thereby increase the purity of the sugar mass without substantial loss of sugar in the wash liquor; and melting the dextrose from the last named crystallizing operation and reusing the same, mixed with fresh dextrose solution, for another crystallizing operation as the process is continued.

2. Process for the production of crystalline dextrose which comprises: crystallizing a dextrose solution; centrifuging the massecuite to remove most of the mother liquor; introducing a wash liquid into the centrifugal machine to remove residual mother liquor; subjecting the first named mother liquor to a crystallizing operation; centrifuging this massecuite to remove most of its mother liquor; introducing into the centrifugal machine. for removal of residual mother liquor therefrom, wash liquid from the first centrifuging operation; and melting the dextrose from the second crystallizing operation and re-using the same, mixed with fresh dextrose solution, for another crystallizing operation as the process is continued.

3. Process for the production of crystalline dextrose which comprises: crystallizing a dextrose solution; centrifuging the massecuite to receive most of the mother liquor; introducing into the centrifugal machine fresh water to remove the residual impurities; subjecting the mother liquor from the first named crystallization to a second crystallizing operation; centrifuging this massecuite to remove most of its mother liquor; introducing into the centrifugal machine liquid from the fresh water washing operation in the rst centrifuging operation, which is substantially supersaturated as to dextrose and has a higher purity than the residual mother liquor of the second massecuite, to displace said residual mother liquor; and melting the dextrose from the second centrifuging operation and using the same, mixed with fresh dextrose solution, for another crystallizing operation as the process is continued.

WILLIAM B. NEWKIRK.

CERTIFICATE OF CORRECTION.

Patent No. 2,129,86L. september 13, 1958 WILLIAM B. NE/JKIRK.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 25, claim 5, for the word receive read remove; and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of October, A. D. 1958.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

